Rotary fillers and filling methods, both within and outside the above definitions, are commonly in use for the filling of containers of many different kinds, with flowable products which may be in the form of free-flowing (low-viscosity) liquids, viscous liquids such as paint, dry solids in powder or granular form, or products containing both solid and liquid. Although the present invention is applicable to all kinds of flowable product and to most kinds of container, it is concerned primarily with the solution of a problem which is found to arise only where high-speed filling is required. Many container filling operations do not call for high filling speeds, and, indeed, a very great variety of products is introduced into containers, such as cans, bottles, flexible tubes, large tins etc., by relatively low-speed fillers whose operation is rotary (in the sense that a succession of containers is moved along a circular path by a turret, and filled during this movement) but which normally have stationary filling heads so that the turret is moved by an indexing mechanism from one station to another in intermittent motion. Such machines are outside the scope of this application and are mentioned only in order to help identify the field of the present invention, which is concerned with high-speed fillers having continuously-rotating filling heads operating on containers which are themselves in continuous rotation.
In a typical rotary filler, of known kinds, whether or not falling within the definition of a rotary filler as set forth hereinbefore, the main turret rotates about a vertical axis and the containers to be filled are carried upright, with their open ends at the top, on and by the rotating turret. Filling takes place primarily by gravity in the case of solids or unpressurised liquids. In the case of liquids to be introduced into the container under pressure (for example beer and other carbonated drink products), the filling head engages against the open end of the container so as to form a pressure seal during the filling operation. Whilst this system works quite satisfactorily at low speeds, problems arise if the speed is increased. In high speed, nonintermittent, rotation, the influence of centrifugal force on the liquid in the container becomes more significant, and the maximum speed of rotation obtainable in practice is consequently limited by the tendency of this force to cause spillage of the liquid at the instant at which the container is transferred to a linear or rotary conveyor leading from the filler to the next stage, which is a closing machine for closing the container. This effect is accentuated when filling takes place under pressure because at the instant when the container is disengaged from the filling head, the release of applied pressure within the container allows centrifugal force to take full effect suddenly, thus greatly increasing the risk of spillage.
If the speed of rotation is further increased, the horizontal, radial, centrifugal acceleration acting on the liquid may become sufficiently great, in relation to the acceleration due to gravity, for the surface of the liquid in the container to become inclined to the horizontal by an angle so steep that spillage will occur at the radially-outward edge of the open end of the container even during the filling operation, i.e. before the container is completely filled. Although this effect can be overcome by mounting the container on the turret at an angle to the vertical such as to compensate for this tilting of the liquid surface, such a solution itself gives rise to further problems in attempting to effect a smooth transition, without spillage, from the tilted attitude of the container during filling to an upright attitude upon its removal from the turret of the filler. A carefully-designed transition path is necessary in order to achieve this, and suitable means must be provided for ensuring that the container is moving at a particular predetermined speed for which the transition path has been designed. The operation of a filler with tilted cans is also itself limited to a single design speed, viz. the particular speed at which the plane of the liquid surface under the influence of centrifugal force is approximately normal to the container axis.